This invention relates to polyurethane foams, more particularly to polyurethane foams which exhibit excellent flame resistance in small scale burn testing. The terms "combustion-modified," "flame resistant" and similar terms as used herein refer to a material's performance in laboratory flammability tests, and are not meant to describe performance under actual fire conditions.
Flexible polyurethane foams are widely used as cushioning material in, for example, furniture, automobile seating, impact-reducing medias, and the like. One concern regarding the use of these foams is their performance under fire conditions, particularly their ability to resist igniting and to extinguishing themselves when exposed to flame.
Many attempts have been made to reduce the flammability of polyurethane foams. The most common method is to incorporate a halogenated compound or phosphate ester flame retarding agent into the foam formulation. These agents have been somewhat successful in reducing the flammability of the foams. However, the use of these flame retarding agents has several substantial drawbacks. Although they are somewhat successful in suppressing flames, under fire conditions they decompose to form toxic gases, particularly gaseous halogen-containing compounds such as HCl and HBr. Foams containing these agents, although they resist flames, sometimes smolder during fires. In preparing the foams, the halogenated flame retarding agents often scorch the interior of the foam, which is believed to cause degradation of the foam properties. In addition, these flame retardants deactivate many of the catalysts used in the foam formulation. Moreover, many companies do not like to introduce halogenated compounds into the workplace for fear of worker exposure. In addition, relatively large quantities of these agents must be used in order to obtain satisfactory results, adding significantly to the cost of the foam.
Other types of flame retardant additives are described in U.S. Pat. No. 4,722,942, which discloses the use of fire retardant additives comprising hydroxyl-terminated alkanes having a plurality of primary hydroxyl groups and alkylene ethers and polyethers having a plurality of primary hydroxyl groups. However, the primary hydroxyl-containing compounds described above are often incompatible with the high molecular weight polyols used in the preparation of polyurethane foams. In addition, the use of these primary hydroxyl-containing compounds also produces foams which have physical properties which are less than desirable for some applications.
In view of the foregoing, it would be desirable to provide a polyurethane foam which does not release halogen-containing gases when burned, which does not present the processing and exposure problems associated with the halogenated and phosphate ester agents, which is compatible with the high molecular weight polyols used in the preparation of polyurethane foams, and which produces foams with better physical properties than those obtainable from the use of the conventional flame retardant additives described above.